Experimental methods in behavior genetics
This chapter is concerned with the details of certain genetical procedures adapted to animal experimentation. Although not an exhaustive account of methods, it describes the procedures most used in psychological genetics and suggests others of potential value which have not yet been widely tested in behavior studies. Our objective is not so much to provide a source for all possible procedures as to facilitate communication between psychologists and geneticists. In order to describe the rationale of some techniques used in the study of the inheritance of quantitative characters, it has been necessary to introduce additional theoretical material from time to time. Unfortunately, the need for conciseness has forced the introduction of some topics before they have been properly discussed in detail. Inbred strains, for example, are mentioned several times before the section on inbreeding. The index has been arranged to facilitate the location of definitions of genetic terms.
Methods have been divided into two classes: (1) those concerned with specific loci; (2) those dealing with the combined effects of genes at many loci. The latter will be referred to as polygenic systems. Whether one deals with single genes or many, two general approaches to psychological genetics are possible. The starting point may be individual variability in behavior, and experiments can be designed to determine whether or not the variations are heritable. If the answer is positive, further breeding experiments are carried out to determine whether the occurrence of the character fits a particular hypothesis of genetic transmission, expressed either in terms of Mendelian units or in the statistical form usual for quantitative characters under polygenic control. The second type of approach starts with two groups of animals known to be genetically unlike and looks for phenotypic behavioral differences between them. Here there is again a choice between working with differences at one or a few named loci and working with